U.S. airlines moved to reassure flyers Monday the Max 8 planes are safe.

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Darryl Coote, Clyde Hughes and Danielle Haynes

Air China passenger jets are parked at gates at Beijing's international airport on Monday, as 96 Boeing 737 Max 8s are grounded. Photo by Stephen Shaver/UPI | License Photo

People wait for passengers at an arrival gate in Beijing's international airport on Monday. Photo by Stephen Shaver/UPI | License Photo

Passengers check-in at a ticket counter in Beijing's international airport on Monday. Photo by Stephen Shaver/UPI | License Photo

Armed security guards watch over travelers one day after the crash of Ethiopian Airways Flight 302 at JFK Airport on Monday in New York City. Photo by John Angelillo/UPI | License Photo

March 11 (UPI) -- China, Indonesia and Singapore on Monday said they're grounding their fleets of the Boeing 737 Max 8 after a crash in Ethiopia killed nearly 160 people.

The Civil Aviation Authority of China said Monday all 96 of its Boeing 737 Max 8s would be taken out of service temporarily under "the management principle of zero tolerance for safety hazards and strict control."

The moves followed the crash Sunday of an Ethiopian Airlines jet immediately after takeoff in Addis Ababa, killing all 157 on board. It was headed for Nairobi, Kenya.

Sunday's was the second crash involving a new 737 Max 8 in less than six months. In October, an Indonesian Lion Air jet crashed a short time after takeoff, killing 189 people.

"In view of the fact that the two air crashes are newly delivered Boeing 737 Max 8 aircraft, and they all occur in the take-off phase, they have certain similarities," China's civil aviation administration said.

The plane's "black boxes" were found Monday near Bishoftu, 40 miles south of Addis Ababa, the airline said. The boxes contain the flight data recorder and cockpit voice recorder, which typically offer valuable clues to the crash.

Boeing said Sunday it was "deeply saddened" by the crash and extended "heartfelt sympathies to the families and loved ones" of the dead.

"A Boeing technical team will be traveling to the crash site to provide technical assistance under the direction of the Ethiopia Accident Investigation Bureau and U.S. National Transportation Safety Board," Boeing said in a statement.

Ethiopian Airlines and Cayman Airways also suspended the use of the 737 models until further notice.

In a tweet Monday, Ethiopian Airlines said it decided to ground the 737 fleet as an "extra safety precaution." Cayman Airways said it would suspend both of its 737 Max 8s.

"While the cause of this sad loss is undetermined at this time, we stand by our commitment to putting the safety of our passengers and crew first by maintaining complete and undoubtable safe operations, and as such, we have taken the decision to suspend operations of both our new Boeing 737 Max 8 aircraft," Cayman Airways President and CEO Fabian Whorms said in a statement.

Whorms said the suspension would cause schedule and flight capacity changes this week.

More than 300 Boeing 737 Max 8 jets are in operation worldwide and 5,000 more have been ordered since 2017.

Southwest Airlines has a fleet of 34 Boeing 737 MAX 8 aircraft and has no plans to ground them.

"We remain confident in the safety and airworthiness of our fleet of more than 750 Boeing aircraft. Our focus on the safety of our operation remains constant and unwavering," Southwest said in a tweet.

Southwest said it's operated about 31,000 flights with the Max 8 and plans on "operating those aircraft going forward." Spokesman Chris Mainz said the airline is in contact with Boeing about the investigation.

American Airlines said it has no plans to ground the two dozen Max 8s in its fleet.

"We have full confidence in the aircraft and our crew members, who are the best and most experienced in the industry," American Airlines tweeted.

The Association of Professional Flight Attendants, which represents more than 27,000 flight attendants at American Airlines, said its members will not be forced to work flights on the Boeing Max 8 aircraft.

"It is important for you to know that if you feel it is unsafe to work the 737 Max, you will not be forced to fly it," said Lori Bassani, president of the union.

In November, unions representing pilots who fly the Max 8s accusing Boeing of not telling them about a new automatic safety feature that pulls down the plane's nose repeatedly, USA Today reported.

United Airlines doesn't have Max 8s in its fleet but does have 14 Max 9s.

"If you prefer not to fly one we completely understand will do what is best in our capabilities to find alternative travel arrangements," the carrier said.